1. Field of the Invention
The present invention relates to an optical waveguide for a touch panel and a touch panel using the same.
2. Description of the Related Art
Touch panels are input devices for operating an apparatus by directly touching a display screen of a liquid crystal display device or the like with a finger, a purpose-built stylus, or the like, and include a display which displays operation details and the like, and detection means for detecting the position (coordinates) of a portion of the display screen of the display touched with the finger or the like. Information about the touch position detected by the detection means is sent in the form of a signal to the apparatus, which in turn performs an operation and the like displayed on the touch position of the display screen. Examples of the apparatus employing such a touch panel include ATMs in banking facilities, ticket vending machines in stations, portable game machines, and the like.
Detection means employing an optical waveguide is proposed as the detection means for detecting the finger touch position and the like on the above-mentioned touch panel (see, for example, U.S. Patent Application Publication No. 2004/0201579A1). Specifically, the touch panel includes optical waveguides provided around a periphery of a display screen of a rectangular display, and is configured to emit multiple light beams parallel to the display screen of the display from an optical waveguide provided on one side portion of the display screen toward the other side portion, and to cause the light beams to enter an optical waveguide provided on the other side portion. These optical waveguides cause the light beams to travel in a lattice form on the display screen of the display. When a portion of the display screen of the display is touched with a finger in this state, the finger blocks some of the light beams. Therefore, the light-receiving optical waveguide senses a light blocked portion, and the position of the portion touched with the finger is thus detected.
By the way, the light beams emitted from an end surface of an optical waveguide directly into the air diverge radially unless the measures are taken. Therefore, there have been proposed various kinds of optical waveguides, which include a core having an end portion formed in a lens-shaped configuration so as to suppress the divergence of the emitted light beams and emit light beam which are collimated as much as possible. An optical waveguide in which the end portion of the core is formed as a lens portion of a special configuration in plan view is known (see JP-A-2009-103902).
In the technology disclosed in JP-A-2009-103902 described above, the lens portion at the end portion of the core of the optical waveguide is of a special configuration in plan view including a tapered portion and an arc portion. By the configuration, divergence of the light beams from a starting point of the lens may be suppressed by the tapered portion, and the light beams may be refracted at the arc portion to bring the light beams into nearly collimated light beams.
However, in a touch panel, the position of a finger which touches the display screen of the display is required to be detected with higher accuracy. In order to respond to the requirement, it is necessary to further enhance the power of gathering light emitted from the end portion of the core.